Which version of the Ki-43 do we want?
The most produced was the Ki-43-IIa which was armed wih 2 12.7mm machine guns, each with 250 rounds. The first prototype Ki-43-IIb first flew in Febuary of 1942.
The Ki-43-I entered production in March, 1941 and came in the Ia (two 7.7mm Type 80 machine guns), Ib (one 12.7mm and one 7.7mm machine gun) and Ic (two 12.7mm machine guns). The Ki-43-I had a top speed of 308mph, no armor and no self sealing tanks.
The Ki-43-II had some armor and self sealing tanks added. The Ki-43-II had a top speed of 320mph and an initial climb of 3,250ft per minute.
All Ki-43s were so lightly built that they broke up when hit, however they also outmanuvered anything else in the air, even A6Ms.
I think the Ki-43-II would be preferable. Its still early war, but has teo 12.7mm guns and so has a hope of actually downing a F4F or P-40.
As to the P-38, I think we need a P-38F. The P-38J is way to modern, being only fractionally older than the P-38L. The P-38J would have no place in an early Pacific Theatre environment. Lets get some contrast before adding versions that are slightly different.